Quenching of metals



Patented Aug. 24, 1943 UNITED STATES PATENT OFFICE Qumonma or un'rsLs .Gillord 0. III Horst, Hampton Township,

. Allegheny County, Blaine B. Weaeott, Chnrchill, and Lealle W. Vollmer, Pittsburgh, Pa" alsignon to Gulf Research a Development Company, Pittsburgh, h, a corporation of Dela- No Drawing. Application January 12, 1942,

Serial No. 426,537

Claims. (CL uas) quenching oil and 1.0 to 20.0 per cent of an oil soluble terpene polymer resin; all as more fully hereinafter set forth and as claimed.

While our invention is useful in the quenching of any metal which is advantageously quenched in an oil bath having a high initial quenchingspeed, it is particularly useful in the quenching of iron base alloys and it will be described hereinafter in detail in connection with the quenching of steel.

Many metal alloys, particularly iron base alloys, such as carbon steels and alloy steels, require heat treatment for the development of maximum properties of hardness and strength. These properties are dependent upon the establishment of certain physical structures in the ,metallic components of the alloy. In steel,

hardenability is determined by the extent to which a martensitic structure is established in the alloy. The production of this structure in steel is usually accomplished by arresting at the desired point, the changes in the internal structure of the alloy which take place during the cooling of the steel from high temperatures. The fact that these physical changes require time for their completion makes it possible to arrest them at the desired point by suitable quick cooling.

Quenching of the steel in aqueous or oil quenching baths is generally used to arrest these physical changes. It is advantageously carried out in such manner that the physical changes in the steel are arrested at or near the point at which maximum hardness is obtained, and is then followed by a tempering treatment involving heating at relatively low temperatures to impart the desired ductility or toughness to the metal at some sacrifice in hardness.

Quenching in aqueous quenching media de- Velops the properties of strength and hardness to the maximum obtainable for a given section of metal. However, quenching in aqueous quenching media is undesirable in many cases because these media tend to set up excessive amounts of internal stress in the steel resulting in distortion and warping and, in the extreme case, cracking of the quenched piece. As a result, aqueous quenching media have been supplanted by mineral oil quenching media where such mineral oil quenching media have sum- ,ciently high quenching speeds to produce the desired properties in the quenched metal because such mineral oil quenching media are particularly adapted to minimize internal stresses and distortion in the quenched product. This results from the fact that the quenching speeds of mineral oil quenching media are substantially slower than those of aqueous quenching media, due to considerable extent to the formation of a more or less persistent vapor envelope about the quenched piece at the beginning of the quenching cycle, and the fact that in the later stages of the quenching cycle the quenching speeds of mineral oil quenching media are sufilciently slow so that the internal stresses developed in the metal in the early stages of the cycle tend to be relieved.

However, since the overall cooling emciency of the mineral oil quenching media heretofore known is not as great as that of aqueous quenching media, it has been diiilcult or impossible to eiTect in mineral oil quenching baths quenching of pieces formed of steels having high critical cooling rates, sufliciently rapidly to develop the properties of strength and hardness to their maximum values or the quenching of pieces having high mass to surface ratios suiliciently rapidly to develop the properties of hardness and strength to the maximum depth.

It is desirable therefore to improve the quenching of metals in mineral oil quenching media so that the cooling eillciency in the early stages of the quenching cycle is increased to more nearly approach the cooling efliciency or aqueous quenching media without increasing the quenching speed in the later stages of the cycle sufiiciently to deleteriously affect the normal stressrelieving properties of the mineral oil.

It is an object achieved by the present invention to provide a method of quenching metals, particularly iron base alloys, in mineral oil quenching media having initial quenching speeds greater than the mineral oil quenching media heretofore known. It is a further object achieved by the present invention to provide mineral oil quenching compositions having cooling efllciencies more nearly approaching the cooling efliciency of water while retaining the stress-preventing characteristics of oil quenches.

The critical cooling rate of ametal is defined as the lowest cooling rate at which maximum hardness is developed. For steel the critical cooling rate is the lowest cooling rate which will produce a full martensitic structure in the steel. Thus it is generally most desirable to effect initial quenching at a speed sufficient to produce a cooling ratelat least equal to the critical cooling rate for as great a depth in the metal as possible and to effect the quenching with a minimum of distortion.

The cooling emciency of a quenching medium is customarily defined in terms of quenching speed and the initial five second quenching speed is a convenient measure of this property of quenching oil compositions, which is the property with which this invention is most concerned. The initial five second quenching speed of a quenching oil composition as referred to throughout this specification and in the appended claims is determined according to the following formula: v

Temperature rise in 5 sec. test Temperature rise in cold quench test in which the respective values are measured as follows:

Cylindrical test pieces one inch in diameter and 2.5 inches long of stainless steel containing about 18.0 per cent of chromium and 8.0 per cent nickel are heatedfor one hour at 1500 F. in a furnace equipped with an automatic temperature control. Two quarts of the quenching oil Per cent available heat re x100 moved in first five sec composition to be tested areplaced in a calorim-,

eter which has a wire screen positioned in the center of the oil bath to insure constant depth of immersion of the samples. The quenching composition is heated to an initial temperature of 100 F.

One of the preheated test pieces is immersed in the quenching bath by means of light tongs for a period of five seconds without agitation. The test piece is then removed and the bath agitated and the maximum temperature reached is measured. A second preheated test piece is immersed in the bath at an initial temperature of 100 F. and the bath is agitated until the maximum rise in temperature has been produced. The maximum temperature rise measured in this cold quench represents the available heat of the test piece. By substituting the values thus determined for the five second quench and for the cold quench in the above formula a measure of the heat removed in the first five seconds as compared with the total available heat is obtained and is referred to herein as the initial five second quenching speed.

We have discovered that oil-soluble terpene polymer resins have the property, when incorporated in a light mineral oil such as has been used heretofore in the quenching of metals, of substantially increasing the initial five second quenching speed of such an oil without lessening its stress-reducing characteristics, and that by incorporating such terpene polymer resins in mineralquenching oils even in amounts as small as 1.0 per cent substantial increases in the initial five second quenching speeds ofthe oils can be produced. Furthermore, we have found that the addition of these terpene polymer resins to the mineral quenching oils does not deleteriously af- In this way the hardness of metals having high critical cooling rates can be developed to a degree heretofore unattainable with mineral oil quenching media, and .hardening can be effected to a greater depth in pieces having high ratios of mass to surface. Both of these results can be achieved with a minimum of distortion.

The various terpene polymer resins do not increase the initial five second quenching speed of a mineral oil in the same degree. Some are more effective than others and also some are more oil-soluble than others and may be used in larger amounts. We have found also that in most cases the effect of each terpene polymer resin increases directly with the amount used, up to a maximum and then decreases. Consequently, the optimum range of concentration for different terpene polymer resins will differ. In general we have found that amounts of terpene polymer resins between about 1.0 and 20.0 per cent by weight effect substantial increases in the initial five second quenching speed of an oil. By use of the proper resin in suitable amount substantially any initial five second quenching speed between about 20.0 per cent and 37.0 per cent can be obtained. It is possible therefore by suitably compounding quenching oil compositions according to our invention to provide a quenching medium which has an initial five second quenching speed particularly adapted to give best results with the particular metal and the particular type of piece being quenched. For most purposes it is advantageous to use a quenching composition having an initial five second quenching speed of at least about 30.0 per cent and for this reason we find it most advantageous to use the terpene polymer resins in amounts corresponding to at least about 3.0 per cent by weight of the oil.

I In compounding the quenching oil compositions of our invention we select for the quenching bath feet the stress-relieving properties which normally a mineral oil of the type customarily used for quenching steel and other metals and these oils are referred to herein as mineral quenching oils. The oils used for this purpose may be either naphthenic or paraffinic oils and are usually acid treated neutral oils having a viscosity of about 70 to 200 S. U. V. at F., relatively high flash and fire points, and substantial heat stability and resistance to sludging. For optimum results we have found that paraifinic oils which usually have an initial five second quenching speed between about 17.0 and about 19.0 per cent are most advantageous.

We have found also that mixtures of the quenching accelerating agents of our invention may be used. However, in such case, the effect of the respective agents is not entirelyadditive and the optimum amounts of the respective agents, when used alone, may produce less satisfactory results in mixtures than do somewhat smaller amounts of each agent.

The actual quenching operation using the quenching compositions of our invention is usually carried out by'immersion of the preheated metal in thequenching oil composition until sufiicient heat has been removed to reduce its temperature the desired amount. The quenching oil may be used repeatedly with only slight deterioration.

The terpene polymer resins which have been found suitable for the purposes of our invention are such as may be obtained by the polymerization of terpenes such as alpha pinene in the presence of a catalyst such as aluminum chloride, zinc chloride and the like. In commercial production, these polymers are customarily produced by the polymerization of pine extracts such as pine oil, turpentine and related materials. One type of resin which has been found suitable may be prepared by the method described in United States Patent No. 1,938,320 of Samuel W. Cooper, in which a relatively pur high boiling fraction of spirits of turpentine dissolved in an inert solvent is treated at a relatively low temperature with aluminum chloride to eil'ect polymerization, the

product is washed with water or dilute hydro-- chlorlc acid to remove the catalyst and undesired reaction products, is fractlonally distilled and the desired resin fraction is recovered. However, terpene polymer resins obtained by other methods may also be used.

Typical terpene polymer resins which we have found suitable exhibit the following physical properties:

proportions in a neutral paramnic mineral oil having a viscosity of 100 S. U. S. at 100 F. The initial five second quenching speeds of the respective compositions were then determined as above described and the following results were obtained:

Initial five 0il+20. e terpene resin A In a second series oftests two more highly refined terpene polymer resins having the properties shown above in Table I were used. One was incorporated in varying quantities between 1.0 and 15.0 per cent in a mineral oil such as has been used heretofore in quenching metals and the other was incorporated in corresponding amounts in four different mineral oils suitable for quenching metals. The several mineral oils used in this test had the following characteristics:

Viscosi S. U. 8. Table 1 at fair E. Type Te -pane Tgrpene Oil N0. 1 7O Neut. paraiiinic.

resin resin 0 il N0 2.- 100 Do Oil No. 3 200 Do. 011 N o. 4 100 Naphthenic. Melting range 0.) 140-150 120430 Ash (per cent max.) 0.05 0.05 gold 1 1 1 11ex 2 l 1.0 I 1.0 The quenching oil compos1t1ons made up in this 22 0 60 manner were tested for quenching speed and the Specific gravity 0.98 -9 following results were obtained:

Not saponiiiable. Initial five second quenching speed The terpene polymer resins when incorporated R in amounts of 1.0 to 20.0 per cent in mineral oils 38in TM 1' B Te'pemi P r tb t. pene 85in such as have been used heretofore in quenching e can yw C metals produce quenching media having initial 1 0111 012 01a 4 five second quenching speeds of at least about 1 l on on 20.0 per cent.

0.0 16.98 10. 01 14.00 1 -In the following examples there are illustrated 1.0 22.92 22. 74 specifically several of the more advantageous gig g 20-07 29-46 1.01 26. 72 34.24 forms of our invention and the results obtainable 4.0.. 34.11 32.10 27.56 35.28 thereby. e21 A terpene polymer resin was P pared accord- 10. 35142 33133 201 87 12. 34.00 33.20 25.16 sacs ing to the method of Cooper U. S. 1,938,320 as 15 3M1 30 50 2239 34.11 follows:

Crude turpentine was distilled through a packed column having an efficiency of approximately 45 plates and a fraction having a boiling range of 155 to 157 C. was recovered. The fraction was mixed with an equal volume of carbon tetrachloride and the mixture was cooled to a temperature less than 1 C. Aluminum chloride in an amount corresponding to about 20 per cent by weight of the turpentine was then added in small increments over a period of 10 minutes so that the temperature, which tended to rise, was maintained relatively close to the starting temperature. The mass was then agitated for a half hour to complete the reaction.

Ice was then added to the reaction mass to destroy any residual aluminum chloride and it was washed several times with caustic soda solution and with water. The washed product was then distilled under 4 cm. vacuum up to 140 C. The terpene resin product remaining after the distillation was used in compounding quenching oils.

Quenching oil compositions were made up by incorporating the resin thus obtained in various As will be seen from these results, by the use of different amounts of difierent terpene polymer resins, quenching speeds from about 20.0 to about 37.0 per cent are obtainable. Also, it will be noted that in each case the concentration required for the highest quenching speed passes through an optimum range. Also, these resins are substantially less effective with naphthenic oils than withparafllnic oils when used in corresponding amounts.

Hardness and distortion tests were made on pieces of metal quenched in the quenching composition consisting of mineral oil No. 2 and 4.0 per cent of terpene resin B. These measurements were made on specially designed pieces adapted to show, measurably, very small changes in shape due to distortion and having a continuously changing section which permitted measurement of the variation in surface hardenability with varying section of the pieces, and thereby gave an indication of the variation in depth of hardening of the piece. The changes in shape were measured in inches and the and 1 minimum Brinell hardness occurring atfd'ifle'rent points on the surface of the piece ;wero,determined. Comparative tests were made on pieces j quenched in water or in the mineral, oil alone.

Results 0! the distortion measurements are shown.in the following table:

" Change in Quenching medium i dim nsion Pf'g Tap water. +0. 0134 .7 +0. 0102 +0. 0116 011 N0. 2 i +0- 0032 .I +0. 0024 +0.00% Oil No. 2 and 4% terpene resin B +0. 0021 +0- Results of s the hardness' measurements are shownin the following table:

g H Surface Brincll hardness Quenching medium v I Minimum Maximum Variation Tap water 649 723 I 74 as 0. an 2 one i resin 3 full.-- 645 716 70 From these results it will, be observed that while tap water gives the greatest surface hardness and a variation 0! only '74 pointsfrom the hardest. to the softest area, it also givesmaximum-distortion. The mineral oil alone :minimizes distortion, but gives a lowered surface about -1.0 per, centaby weight of bodiments thereof, it is to be understood ,that,it; V

oil "an initial flve second quenching speed"ofiatleast about 20.0 "per' cent without. substantially modifying the stress reducing characteristics ofthe oil. 1

3 .-;A-method. of quenching .metals comprising L heating the: metal to a temperature-above its critical temperature and thereafter cooling; the metal by:-immersion in a quenching oil bath'comprising a mineral quenching oil andan'am'ount of an oil-soluble terpene polymer resin, above about 1.0 per cent adequate to impart'to-rtheiquenching oil bath-an initial five second quench-1 ing speed of 'at' least about 20.0 per cent.

4. An improved quenching oil Y composition comprising a solution of at least 3 per centby' weight of an oil soluble terpene polymer resin in a mineral quenching oil.

5. Ana improved quenching oil composition comprising a mineral quenching oil and-an on soluble 'terpene' polymer ,,..resin in, controlled amount, adequate to impart to said quenching hardening and a variation of 335 points from the maximum to the minimum area indicating a non-uniform depth of hardening throughout the piece. On the other hand, the specimen quenched according to our invention is a quenching oil composition having an initial five second quenching speed of about 35.28 per cent showed distortion as low as that obtained with the plain mineral oil, a surface hardness as high asthat obtained with water and a variation in surface hardness no greater than that obtained with water, indicating a depth of hardening approaching to that obtainable with the water quench.

While we have particularly described our invention with reference to certain specific emoil an initial 5 second quenching speed ofabout; V 30 to 37 percent without substantially modifying the stress reducing characteristics of the oil. 6. A method of quenching metals -"com-' prisingheating the metal to a temperature above its critical temperature and thereafter cooling the metal by immersion in'a quenching oil bath comprising a mineralquenching oil and an amount of an oil soluble terpene polymer resin above about 3 per cent, adequate to impart to-the quenching oil bath an initial 5 second quenching speed between about 30 and 37 per cent.

' I CLIFFORD G. m HORST."

BLAINE B.- WESCO'I'I. LESLIE W. VOLLMER. 

